1. Technical Field
The invention relates to a projection type zoom lens which is mounted in a projection type display apparatus and the projection type display apparatus, and more particularly to a projection type zoom lens and a projection type display apparatus with temperature compensation being taken into consideration.
2. Description of the Related Art
In recent years, projection type projectors have been widely used, for example, at presentation situations. There has been a demand for further improvement in performance particularly in terms of chromatic aberration along with higher resolution of images which are supplied from personal computers or the like. It has been known that it is effective for correction of the lateral chromatic aberration in a projection lens of the projection type projector to use a glass material having an anomalous dispersion property as a positive lens (e.g. see JP 2004-117519 A). However, the anomalous dispersion glass material is opposite in sign of a temperature coefficient of a refractive index to a normal glass material. Therefore, if the power of the positive lens is made stronger, the point of focus would deviate.
In particular, in the projection type projector, a high-output light source is used. Therefore, heat from the light source is transmitted to a lens barrel through a mount and warms the lens. In addition, the light from the light source is radiated to a lens holding frame, a diaphragm, a barrel chamber, and the like and generates heat. Since the lens is warmed by this heat as well, the temperature of the respective lens elements increases substantially. Accordingly, since the powers of the positive lens cannot be made very strong, it is difficult to correct the lateral chromatic aberration substantially.
On the other hand, in an optical system of the projection type projector, as a technology for alleviating the deviation of the point of focus due to increase of temperature, it has been known to use a compound aspherical lens as a projection lens (see JP 2003-195169 A (corresponding to U.S. Pat. No. 6,738,196)). The compound aspherical lens is one in which a thin plastic aspherical lens is cemented to a glass spherical lens. The deviation of the point of focus due to the plastic lens sensitive to a temperature change is alleviated by making the plastic lens thin. However, this technology alleviates the deviation of the point of focus due to the plastic lens and, of course, it does not essentially resolve the deviation of the point of focus associated with the temperature change in the case where the anomalous dispersion glass material is used as described above.
In view of these circumstances, in the projection lens of the projection type projector, there has been a demand for a technology for a simple configuration which makes it possible to effectively improve chromatic aberration by using an anomalous dispersion glass material and to improve the deviation of the point of focus associated with a temperature change in the case where the anomalous dispersion glass material is used.
In an imaging lens system of a fixed focus type, although not a projection lens of a projection type projector, the following technology has been known (JP 2003-222793 A (corresponding to U.S. Pat. No. 6,747,815)). Chromatic aberration is corrected by using a positive lens made of a glass material having an anomalous dispersion property, and the deviation of the point of focus associated with a temperature change, which occurs due to the use of this positive lens, is offset by using a negative lens made of a glass material having an anomalous dispersion property.
However, the technology of JP 2003-222793 A is applicable to an imaging lens system such as a television lens, and is not assumed to be used in a lens system whose temperature changes substantially as in the projection lens of a projection type projector. In addition, since the applicable object is a fixed focus lens, the configuration provided is not such that it takes into consideration the change in the relative positions of the lens groups during zooming.